The compound 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (also known as THIP or gaboxadol, and hereinafter referred to as gaboxadol) and is a known GABAA receptor agonist (see, for example, EP 0 000 338) and has therefore been suggested for use in treating a variety of neurological and psychiatric disorders such as epilepsy, Parkinson's disease, schizophrenia and Huntingdon's chorea. More recently, there has been disclosed the use of gaboxadol for treatment of sleep disorders (WO 97/02813) and premenstrual syndrome (WO 02/40009), and the disclosure that gaboxadol is a particularly potent agonist at GABAA receptors comprising α4 and δ subunits (Brown et al, British J. Pharmacol., 136, 965-74 (2002).
Other indications for which gaboxadol may be suitable include hearing disorders (especially tinnitus), vestibular disorders, attention deficit hyperactivity disorder, intention tremor and restless leg syndrome.
The preparation of gaboxadol is disclosed in EP 0 000 338, both as the free base and as an acid addition salt (specifically, the hydrobromide), but here is no mention of hydrated forms, and the hydrobromide was the form used for the pharmacological testing described in EP 0 000 338.
Gaboxadol is sold commercially (eg. by Sigma) in the form of the hydrochloride salt, and WO 01/22941 and WO 02/094225 disclose granulated pharmaceutical compositions comprising gaboxadol in the form of the hydrochloride salt.
As detailed in WO 02/094255, use of acid addition salts of gaboxadol such as hydrochloride in the manufacture of pharmaceutical oral dosage forms such as tablets gives rise to corrosion problems when conventional techniques and equipment are employed. There is therefore a need for novel forms of gaboxadol suitable for incorporation in pharmaceutical oral dosage formulations.
Morphological forms of pharmaceutical compounds may be of interest to those involved in the development of a suitable dosage form because if the morphological form is not held constant during clinical and stability studies, the exact dosage used or measured may not be comparable from one lot to the next. Once a pharmaceutical compound is produced, it is important to recognize the morphological form delivered in each dosage form to assure that the production process uses the same form and that the same amount of drug is included in each dosage. Therefore, it is imperative to assure that either a single morphological form or some known combination of morphological forms is present. In addition, certain morphological forms may exhibit enhanced thermodynamic stability and may be more suitable than other morphological forms for inclusion in pharmaceutical formulations. As used herein, a polymorphic form of a chemical compound is the same chemical entity, but in a different crystalline arrangement.